It is often desirable to proceed to a sulfurization (generally called "presulfurization") of the metals contained in certain refining and/or hydrocarbon hydroconversion catalysts, either when fresh catalysts are concerned, or at the end of the regeneration step of said catalysts, before reusing them.
A presulfurization of fresh or regenerated catalysts is thus desirable when using these catalysts in refining reactions, for example the reactions of desulfurization or hydrodesulfurization of various gasolines, for example catalytic cracking or steam-cracking gasolines, whose sulfur content has conveniently to be decreased before use, without modification of the less possible modification of the octane number of said gasolines. Such desulfurization reactions are generally conducted in the presence of hydrogen, from 200.degree. to 400.degree. C., under a pressure from, for example, 5 to 60 bars, at a space velocity (expressed in m3 of introduced liquid charge per m3 of catalyst and per hour) from 0.5 to 15, with a hydrogen partial pressure from 4 to 60 bars, the charge being for example a gasoline generally distilling between 30.degree. and 220.degree. C. and whose bromine number may range from 40 to 80 (g/100 g), containing about 15-45% by volume of olefins (essentially monoolefins--very small amounts of diolefins) and 15-25% of aromatic hydrocarbons.
The catalyst used in this type of desulfurization or hydrodesulfurization comprises a carrier, generally non acidic, for example an alumina or mixtures of aluminas (U.S. Pat. No. 4,334,982) or any other suitable carrier mainly of at least one metal or metalloid oxide (magnesia-U.S. Pat. Nos. 4,132,632, 4,140,626), silica, silica-aluminas, silica-magnesiae, fluorinated silicas, boron aluminas, clays, coals. fluroinated aluminas). This or these carrier mixtures may be at least partly in amorphous or crystallized form (zeolites) and the catalyst may further contain 0.2 to 30% of at least one active metal from groups VI, VIII or another metal selected for example from the group consisting of cobalt, molybdenum, nickel and tungsten (U.S. Pat. Nos. 3,732,155 and 3,804,748). Generally, these metals are used by pairs, for example one of the following pairs: cobalt-molybdenum, nickel-molybdenum, cobalt-tungsten, tungsten-molybdenum, cobalt-nickel, nickel-tungsten. Still by way of example, there can be used a noble metal from group VIII of the platinum family: Pt, Pd . . . (U.S. Pat. No. 4,098,682).
Thus, before being used, the catalyst, fresh or regenerated, is generally subjected, in the prior art, to a sulfurization (presulfurization) conducted in a hydrodesulfurization reactor. By said sulfurization it is possible to introduce in the catalyst, for example, about 50 to 110% of the sulfur stoichiometrical amounts calculated on the sulfide amounts of formulas (according to the metals involved): Co.sub.9 S.sub.8 Mo S.sub.2, WS.sub.2 and Ni.sub.3 S.sub.2.
This sulfurization (presulfurization) is conducted, in the prior art, at a temperature substantially equal or higher than the reaction temperature (thus higher than 180.degree. C. and more particularly above 250.degree. C.) selected for the hydrodesulfurization reaction, for a few hours, by means of a mixture of hydrogen sulfide generally diluted in hydrogen (proportion of hydrogen sulfide in hydrogen of about 0.5-5% by volume) with a convenient space velocity, for example from about 1000 to 3000 liters of gas under normal temperature and pressure conditions per liter of catalyst and per hour (U.S. Pat. No. 4,334,982). The sulfurization (or presulfurization) itself may be conducted by temperature steps (French Pat. No. 2 476 119). Various sulfurization agents other than hydrogen sulfide (H.sub.2 S) may be used, for example a sulfur compound of the mercaptans family, carbon sulfide (CS.sub.2), sulfides or disulfides, thiophenic compounds and preferably dimethylsulfide (DMS) or dimethyldisulfide (DMDS).
A sulfurization or presulfurization of the regenerated catalyst is also desirable in hydrocarbon hydroreforming reactions (particularly naphtha reforming) and in the production of aromatic hydrocarbons ("Aromizing") for example the production of benzene, toluene and xylenes (ortho, meta or para), either from unsaturated or saturated gasolines (for example pyrolysis, cracking, particularly steam-cracking, or catalytic reforming gasolines) or still from naphthenic hydrocarbons which, by dehydrogenation, can be converted to aromatic hydrocarbons.
The general conditions of these reactions are generally as follows: average temperature from 400.degree. to 600.degree. C., pressure from 1 to 60 bars, hourly velocity from 0.1 to 10 volumes of liquid naphtha per volume of catalyst and recycle rate from 0.5 to 20 moles of hydrogen per mole of charge.
The catalyst may contain for example, at least one metal from the platinum family, i.e. a noble metal such as platinum, palladium, iridium, rhodium, ruthenium, osmium, deposited on a convenient carrier (alumina, silica, silica-alumina, fluorinated aluminas, fluorinated silicas, zeolite etc. or mixtures of said carriers). The total content of noble metals ranges for example from 0.1 to 5% by weight, with respect to the catalyst. The catalyst may also contain generally at least one halogen (chlorine, fluorine etc.) in a proportion by weight from 0 to 15%. Still optionally, the catalyst may contain a least one promoter metal selected from the various groups of the periodic classification of elements, the proportion by weight of promoter metal varying for example from 0.1 to 15%. Examples of such metals are those from groups VIII, VI A and VI B, I B and II B, III A, IV A, V A and V B, IV B, III B, I A and I B, as well as the metals of the lanthanide family; more particularly, in addition to the noble or non noble metals from group VIII, copper, silver, gold, germanium, tin, indium, thallium, manganese, rhenium, tungsten, molybdenum, niobium and titanium are of interest.
For these reactions of catalytic reforming or aromatic hydrocarbons production, the sulfurization of the fresh or regenerated catalyst is accompanied with a reduction with hydrogen of the catalyst and takes place at the top of the reactor or in the vicinity thereof. The temperature in the sulfurization zone is determined by the temperature at which the reduction takes place, i.e. mostly between 480.degree. and 600.degree. C. The difficulty in this type of sulfurization on the site, i.e. at the vicinity of the reactors, has often led to time-consuming, although efficient sulfurization operations (U.S. Pat. No. 4,172,027).
The sulfurization agent used in the prior art is either hydrogen sulfide, pure or diluted with hydrogen or with gaseous hydrocarbons, or dimethyldisulfide diluted with hydrogen, or other sulfur compounds such as alkyl sulfides or alkylmercaptans, diluted with hydrogen. The pressure is that prevailing in the reforming reactor or the reactor for aromatic hydrocarbons production, the reaction time varying from a few minutes to a few days according to the selected operating conditions (see U.S. Pat. No. 4,172,027).
A sulfurization (presulfurization) of fresh or regenerated catalyst is sometimes still convenient for the partial or total sulfurization of the catalyst, also using one of the above-mentioned carriers and at least one of the already mentioned active metals convenient for the reactions of hydrocarbon conversion such as hydrogenation, dehydrogenation, alkylation, hydroalkylation, steam-dealkylation, isomerization and hydrodemetallization (or demetallation) of heavy charges.
The sulfurization or presulfurization, when necessary, may be advantageously performed according to any one of the above-indicated prior art techniques.
The metals of the catalysts used in refining, hydrorefining and petrochemistry, either fresh or regenerated, are mostly in oxidized form, sometimes in metal form, particularly for certain metals of reforming catalysts. Now, the metals of said catalysts are often active only in sulfurized or at least partially sulfurized form. It is hence necessary, for the refiner or the petrochemist to proceed to a sulfurization of the catalyst before using it.
Presently, the regeneration of the catalysts is more and more performed by a specialist of said catalyst regeneration, at a location sometimes far from the industrial unit. Now, it seems reasonable to provide to the refiner a product ready for use, after regeneration. This is possible by the efficient process disclosed in the European patent application No. 84 400 234 wherein the sulfur compound is incorporated to the catalyst mass so as to sulfurize or presulfurize the catalyst when, subsequently, in the reaction zone (zone of the charge treatment) or in the immediate vicinity thereof, the catalyst will be contacted with hydrogen. Of course, said sulfur compound may be, if desired, incorporated at the vicinity of the industrial unit or even on the mere location of the catalyst treatment unit: the process for incorporating said sulfur compound may be conducted out of site also on a fresh or regenerated catalyst, before its use in an industrial unit.
More precisely, according to the European patent application No. 84 400 234, the process for sulfurizing the catalyst is hence characterized by a preliminary step called step of incorporation in the catalyst mass of a sulfur compound of a particular nature.
The preliminary step of introducing a sulfur compound, arbitrarily called "out of site" or "ex situ" pretreatment, either performed at the vicinity of the industrial unit site or at a location more or less far from the industrial unit (at the location where the catalyst has been regenerated or where it has been manufactured, for example) in any way no longer takes place in the immediate vicinity of the reactor (arbitrarily referred to as "in situ") i.e. at the top of the reactors or zones more or less directly communicating with said reactors, requiring the use of operating conditions (temperature, pressure or others) at least partly dependent on the operating conditions of the reactors themselves or of ancillary elements of said reactors (for example, zone of preliminary hydrogenation of the catalyst).
In short, the invention of the European patent application No. 84 400 234 concerns a process whereby, when subjecting the catalyst, as soon as the beginning of its operation, preferably on the site ("in situ") to the conventional activation reaction in the presence of hydrogen (generally above 100.degree. C.), it will be then possible, by means of the hydrogen present on the site, to sulfurize to the required extent (stoichoimetrical or non stoichiometrical), the one or more active metals contained in the catalyst. The process consists of incorporating, in the absence of hydrogen, in the pores of the fresh or regenerated catalyst, at least one sulfurization agent of general formula: EQU R--S .sub.(n) --R'
wherein R, R' and n are defined hereinafter.
The sulfurization of the catalyst may thus be performed as follows: in a first step performed "ex situ", in the absence of hydrogen, the catalyst is treated with at least one sulfurization agent so as to partially or completely incorporate said agent in the catalyst pores, the sulfurization agent being a polysulfide of general formula: EQU R--S .sub.(n) --R'
said sulfurization agent being used in solution in a solvent; in a second step, performed "in situ" and preferably above 150.degree. C., the catalyst is activated in the presence of hydrogen, the required sulfur amount being fixed, owing to the presence of hydrogen, on the one or more metals contained in said catalyst. This last step is the one which is improved according to the present invention.
The object of the European patent application No. 84 400 234 is hence to conduct "ex situ" the presulfurization of the catalyst by incorporating the whole required sulfur amount and only the sulfur amount required by the user. Accordingly, the catalysts delivered to the refinery or to any other unit are preconditioned in view of being presulfurized.
The refiner, or any other user, thus have only to reactivate said catalyst in the presence of hydrogen at a temperature of, for example, from 100.degree. to 200.degree. C. for a desulfurization catalyst, from about 400.degree. to 600.degree. C. for a catalytic reforming or aromatic hydrocarbon production catalyst, so as to cause sulfur to react with the contained metals and start immediately the refining or hydrocarbon conversion reaction by injection of the charge to be treated.
In the polysulfide of formula R--S.sub.(n) --R', n is an integer from 3 to 20, preferably from 4 to 8, more particularly from 5 to 7; R and R', identical or different, represent organic radicals each of which contains 1 to 150 carbon atoms per molecule, preferably either 10 to 60 carbon atoms or 5 to 40 carbon atoms and more particularly 7 to 16 carbon atoms, these radicals being selected from the group consisting of alkyl radicals either saturated or unsaturated, linear or branched, or of the naphthenic type, aryl radicals, alkylaryl radicals, arylalkyl radicals, these various radicals optionally comprising at least one hetero-atom. R' may optionally be also a hydrogen atom.
A preferred example of polysulfide is ditert-dodecylpolysulfide (n=5) wherein R and R' are each a dodecyl radical.
This product is sold on the trade, for example, by ELF AQUITAINE under reference TPS 32, particularly since it contains about 32% by weight of sulfur.
Another example is ditert-nonylpolysulfide (n=5) wherein R and R' are each a nonyl radical.
This product is sold by ELF AQUITAINE under reference TPS 37, particularly since it contains about 37% by weight of sulfur or by PENWALT under reference TNPS.
For reasons of procedure this sulfurization agents of the polysulfide type may be used alone or admixed together in judiciously selected proportions.
The first step, as above recalled, is performed in the absence of hydrogen and provides, with a great accuracy, for the total or partial sulfurization degree required by the user. This sulfur incorporation is conducted between 0.degree. and 50.degree. C., preferably between 10.degree. and 35.degree. C., and more preferably at room temperature.
The sulfurization agent is diluted in a suitable solvent which depends particularly on the nature of the sulfurization agent, i.e. on R or R', radicals which determine the sulfur content incorporated with the catalyst, generally by capillarity or by porosity. The sulfurization processes vary in fact according to the cuts to be subsequently treated in the presence of the catalysts treated according to the invention. The selected solvent may thus be one of the following solvents used alone or admixed together:
a light gasoline boiling for example between about 60.degree. and 95.degree. C., PA1 a gasoline of hexane type boiling between about 63.degree. and 68.degree. C., PA1 a gasoline of F type boiling between about 100.degree. and 160.degree. C. and generally containing 10-20% of aromatic hydrocarbons, for example 15%, by volume, PA1 a gasoline of "white spirit" type boiling between about 150.degree. and 250.degree. C. and generally containing 14-22% of aromatic hydrocarbons, for example 17% by volume, PA1 or any hydrocarbon or non hydrocarbon cut equivalent to the preceding gasolines. PA1 a light gasoline boiling for example between about 60.degree. and 95.degree. C., PA1 a gasoline of the hexane type boiling between about 63.degree. and 68.degree. C., PA1 a gasoline of F type boiling between about 100.degree. and 160.degree. C. and generally containing 10-20% of aromatic hydrocarbons, for example 15% (by volume), PA1 a gasoline of the "white spirit" type, boiling between about 150.degree. and 250.degree. C. and generally containing 14-22% of aromatic hydrocarbons, for example 17%, by volume, PA1 any hydrocarbon or non-hydrocarbon cut, equivalent to the preceding gasolines.
Later, on the site or in the vicinity thereof (site where the catalyst will be used for the treatment of various charges) during the conventional activation reaction, performed in the presence of hydrogen (second step of the process of the European patent application No. 84 400 234), the sulfurization agent introduced into the catalyst in predetermined amounts will be capable to give rise to hydrogen sulfide which, in the presence of hydrogen, will give the desired sulfide or sulfides of the one or more metals present in the catalyst, according for example to the following schematic reactions (1) (2) (3) as far, for example, as sulfurizations of molybdenum, cobalt and nickel are concerned. EQU MoO.sub.3 .fwdarw.MoS.sub.2 EQU 9 CoO.fwdarw.Co.sub.9 S.sub.8 EQU 3 NiO.fwdarw.Ni.sub.3 S.sub.2
By the use of a suitable solvent, wherein the sulfurization agent is dissolved, it is possible to take advantage of the latent vaporization heat of the selected solvent to absorb at least a part of the exothermicity of the sulfurization reaction.
After the sulfur deposit, at least a portion of the solvent remains in the catalyst. It is thus possible to remove said solvent (by stripping with liquid nitrogen for example or by any other means). However, said solvent retained in the catalyst may be removed subsequently without any damage, within the reactor where the catalyst is used, i.e. on the site ("in situ").
In the first step, the volume of polysulfide and of selected solvent must be preferably substantially equal to the pore volume of the catalyst bed to be treated: thus, for example, for 100 g of regenerated or fresh catalyst (oxidized form) about 9 g of sulfur, as polysulfide, are to be introduced into about 45 cc of total mixture polysulfide+solvent (e.g. white spirit). The adsorption of said polysulfide generally takes place in ambient air. The catalyst is then optionally dried in hot air stream, then conditioned in order to be dispatched, according to a preferred method, to the refiner.